Overview of moment-tensor inversion of microseismic events

Abstract

Understanding the source mechanisms of microseismic events is important for understanding the fracturing behavior and evolving stress field within a reservoir, knowledge of which can help to improve production and minimize seismic risk. The most common method for calculating the source mechanisms is moment-tensor inversion, which can provide the magnitudes, modes, and orientations of fractures. An overview of three common methods includes their advantages and limitations: the first-arrival polarity method, amplitude methods, and the full-waveform method. The first-arrival method is the quickest to implement but also the crudest, likely producing the least reliable results. Amplitude methods are also relatively simple but can better constrain the inversion because of the increased number of observations, especially those using S/P amplitude ratios. Full-waveform methods can provide results of very good quality, including source-time functions, but involve much more complex and expensive calculations and rely on accurate seismic-velocity models.